Sheet structure, semiconductor device and method of growing carbon structure

ABSTRACT

The sheet structure includes a plurality of linear structure bundles including a plurality of linear structures of carbon atoms arranged at a first gap, and arranged at a second gap larger than the first gap, a graphite layer formed in a region between the plurality of linear structure bundles and connected to the plurality of linear structure bundles, and a filling layer filled in the first gap and the second gap and retaining the plurality of linear structure bundles and the graphite layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 12/856,031,filed Aug. 13, 2010, which is a Continuation of InternationalApplication No. PCT/JP2008/053635, with an international filing date ofFeb. 29, 2008, which designating the United States of America, theentire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a sheet structureincluding a linear structure of carbon atoms, a semiconductor device,and a method of growing a carbon structure.

BACKGROUND

The electronic parts used in the CPUs (Central Processing Units), etc.of servers and personal computers, etc. have the structure that a heatspreader of a material of high thermal conductivity, such as copper orothers, is arranged with a thermal conductive sheet of an indium sheetor others provided immediately on the semiconductor element so as toefficiently radiate the heat generated by the semiconductor element.

However, the recent large demand increase of rare metal has raised theprice of indium, and substitute materials which are less expensive thanindium are expected. In terms of physical properties, the thermalconductivity of indium (50 W/m·K) cannot be said to be high. For moreefficient radiation of the heat generated by the semiconductor element,materials of higher thermal conductivities are expected.

In such background, as a material having a thermal conductivity higherthan indium, a linear structure of carbon atoms represented by carbonnanotube is noted. Carbon nanotube has not only a very high thermalconductivity (1500 W/m·K) but also good flexibility and electricconductivity. Carbon nanotube has high potential as a radiationmaterial.

As a thermal conduction sheet, a thermal conductive sheet having carbonnanotubes distributed in a resin is disclosed in, e.g., JapaneseLaid-open Patent Publication No. 2005-150362. A thermal conductive sheethaving carbon nanotube bundles grown oriented on a substrate and buriedin a resin is disclosed in, e.g., Japanese Laid-open Patent PublicationNo. 2006-147801.

Carbon nanotube is noted as an interconnection material to be used insemiconductor devices, etc. The copper interconnection presentlydominantly used in integrated circuit devices has many explicit problemsof reliability degradation, etc. due to electromigration as the devicesare increasingly downsized. Then, carbon nanotube, which has goodproperties, such as good electric conductivity, permissible currentdensity, which is about 1000 times higher than that of copper, ballisticelectron transportation property, etc., is expected as a next generationinterconnection material.

As an interconnection using carbon nanotube, proposals of verticalnanotube interconnections using vias are made (refer to, e.g., M. Nihelet al., “Electric properties of carbon nanotube bundles for future viainterconnects,” Japanese Journal of Applied Physics, Vol. 44, No. 4A,2005, pp. 1626-1628.

The following are examples of related: Japanese Laid-open PatentPublication No. 2006-303240; Japanese Laid-open Patent Publication No.09-031757; Japanese Laid-open Patent Publication No. 2004-262666;Japanese Laid-open Patent Publication No. 2005-285821; JapaneseLaid-open Patent Publication No. 2006-297549; Japanese Laid-open PatentPublication No. 2006-339552; and Japanese Laid-open Patent PublicationNo. 2003-238123.

The thermal conductive sheet disclosed in Japanese Laid-open PatentPublication No. 2005-150362 has carbon nanotubes simply distributed in aresin, and thermal resistances are generated at the joints between thedistributed carbon nanotubes. Carbon nanotube has the characteristicthat the thermal conductivity along the direction of orientation ofcarbon nanotube is minimum, but the thermal conductive sheet disclosedin Japanese Laid-open Patent Publication No. 2005-150362, in which theorientation direction of the carbon nanotubes is disuniform, has failedto make the best use of the high thermal conductivity of the carbonnanotube. In this point, the thermal conductive sheet disclosed inJapanese Laid-open Patent Publication No. 2006-147801 has carbonnanotube bundles grown oriented on a substrate, and can realize higherthermal conductivity than the thermal conduction sheet disclosed inJapanese Laid-open Patent Publication No. 2005-150362.

However, the inventors of the present application examined the thermalconductive sheet disclosed in Japanese Laid-open Patent Publication No.2006-147801 and have found that aggregations and biases take placebetween carbon nanotube bundles when a resin is filled between thecarbon nanotubes with a result that the orientation and the uniformityof the carbon nanotubes are impaired, and the thermal conductivitycannot be realized as expected. In this structure, the radiation in thevertical direction (the direction perpendicular to the surface of thesheet) can be ensured to some extent, but it is difficult to ensure theradiation in the horizontal direction (the direction parallel to thesurface of the sheet). That is, the thermal conductivity of the resin asa whole is about 1 (W/m·K) and is lower by about 3 places in comparisonwith the vertical thermal conductivity of carbon nanotube. The radiationeffect in the horizontal direction is very low.

Preferably, the interconnection material can form not onlyinterconnection structures connected in the vertical direction asdisclosed in M. Nihel et al. but also interconnection structuresconnected in the horizontal direction. However, the horizontalinterconnection using carbon nanotube has not been realized yet becausethere are many difficulties in controlling the horizontal growth of thenanotube, and additionally, it is difficult in terms of the process toform electrode blocks interconnecting the via interconnections and thehorizontal interconnections, which are the starts of the horizontalinterconnections.

SUMMARY

According to one aspect of an embodiment, there is provided a sheetstructure including a plurality of linear structure bundles including aplurality of linear structures of carbon atoms arranged at a first gap,and arranged at a second gap larger than the first gap, a graphite layerformed in a region between the plurality of linear structure bundles andconnected to the plurality of linear structure bundles, and a fillinglayer filled in the first gap and the second gap and retaining theplurality of linear structure bundles and the graphite layer.

According to another aspect of an embodiment, there is provided asemiconductor device including a first interconnection layer formed overa semiconductor substrate, a via interconnection formed of a linearstructure bundle including a plurality of linear structures of carbonatoms, and connected to the first interconnection layer, an insulatingfilm formed over the semiconductor substrate in a region except a regionwhere the via interconnection is formed, coating the firstinterconnection layer, and a second interconnection layer including agraphite layer formed on the via interconnection and on the insulatingfilm.

According to further another aspect of an embodiment, there is provideda method of growing a carbon structure including forming a firstcatalytic metal film over a substrate in a first region, forming asecond catalytic metal film different from the first catalytic metalfilm over the substrate in a second region adjacent to the first region,forming selectively in the first region a first carbon structureincluding a plurality of linear structures of carbon atoms with thefirst catalytic metal film as a catalyst, and forming selectively in thesecond region a second carbon structure including a graphite layer withthe second catalytic metal film as a catalyst.

The object and advantages of the embodiment will be realized andattained by means of the elements and combinations particularly pointedout in the claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the embodiments, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a plan view illustrating a structure of a carbon nanotubesheet according to a first embodiment;

FIG. 1B is a diagrammatic cross-sectional view illustrating a structureof a carbon nanotube sheet according to a first embodiment;

FIGS. 2A-2E are plan views illustrating configurations of carbonnanotube bundles of the carbon nanotube sheet according to the firstembodiment;

FIGS. 3A-3C are diagrammatic cross-sectional views illustrating thestructures of the carbon nanotube sheet according to the firstembodiment;

FIGS. 4A-4C and 5A-5C are cross-sectional views illustrating a method ofmanufacturing the carbon nanotube sheet according to the firstembodiment;

FIG. 6A is a plan view illustrating a structure of a carbon nanotubesheet according to a second embodiment;

FIG. 6B is a diagrammatic cross-sectional view illustrating a structureof a carbon nanotube sheet according to a second embodiment;

FIG. 7 is a diagrammatic cross-sectional view illustrating a structureof a carbon nanotube sheet according to a modification of the secondembodiment;

FIGS. 8A-8C and 9A-9C are cross-sectional views illustrating a method ofmanufacturing the carbon nanotube sheet according to the secondembodiment;

FIG. 10 is a diagrammatic cross-sectional view illustrating a structureof a semiconductor device according to a third embodiment;

FIGS. 11A-11C, 12A-12C and 13A-13C are cross-sectional viewsillustrating a method of manufacturing the semiconductor deviceaccording to the third embodiment;

FIG. 14 is a diagrammatic cross-sectional view illustrating a structureof a semiconductor device according to a fourth embodiment;

FIGS. 15A-15C, 16A-16C and 17A-17C are cross-sectional viewsillustrating a method of manufacturing the semiconductor deviceaccording to the fourth embodiment;

FIG. 18 is a diagrammatic cross-sectional view illustrating a structureof an electronic device according to a fifth embodiment; and

FIG. 19 is a perspective view illustrating a structure of an electronicdevice according to a sixth embodiment.

DESCRIPTION OF EMBODIMENTS A First Embodiment

A carbon nanotube sheet and a method of manufacturing the same accordingto a first embodiment will be described with reference to FIGS. 1A to5C.

FIG. 1A is a plan view illustrating a structure of a carbon nanotubesheet according to the present embodiment. FIG. 1B is a diagrammaticcross-sectional view illustrating a structure of a carbon nanotube sheetaccording to the present embodiment. FIGS. 2A-2E are plan viewsillustrating configurations of carbon nanotube bundles of the carbonnanotube sheet according to the present embodiment. FIGS. 3A-3C arediagrammatic cross-sectional views illustrating the structures of thecarbon nanotube sheet according to the present embodiment. FIGS. 4A-5Care cross-sectional views illustrating the method of manufacturing thecarbon nanotube sheet according to the present embodiment.

First, the structure of the carbon nanotube sheet according to thepresent embodiment will be described with reference to FIGS. 1A and 1B.FIGS. 1A and 1B are respectively a plan view and a cross-sectional viewillustrating the structure of the carbon nanotube sheet according to thepresent embodiment.

The carbon nanotube sheet (the sheet structure) according to the presentembodiment includes a plurality of carbon nanotube bundles (linearstructure bundles) 12 arranged spaced from each other (see FIG. 1A). Inthe gap between the carbon nanotube bundles 12, a graphite layer 14formed on one surface side of the sheet, and a filling layer 16 of aresinous material, etc are formed (see FIGS. 1A and 1B). The fillinglayer 16 is also filled in the gaps in the carbon nanotube bundles 12and the graphite layer 14. The graphite layer 14 is thermally andelectrically connected to the carbon nanotube bundles 12.

The respective carbon nanotube bundles 12 are formed, extended verticalto the surface of the sheet and include a plurality of carbon nanotubes(linear structures of carbon atoms) oriented vertical to the surface ofthe sheet.

The carbon nanotube may be either of a single-walled carbon nanotube ora multi-walled carbon nanotube. The density of the carbon nanotubescontained in the carbon nanotube bundles 12 is preferably 1×10¹⁰tubes/cm² or more in view of the radiation and the electric conduction.The length of the carbon nanotube bundles 12 (the thickness of thesheet) is determined by an application of the carbon nanotube sheet 10and is not specifically defined but can be set preferably at a value ofabout 5 μm-500 μm.

In the carbon nanotube sheet 10 according to the present embodiment, agap is provided between the carbon nanotube bundles 12, and the fillinglayer 16 is formed in the gap. This is for, in forming the filling layer16 between the carbon nanotubes, improving the permeation of the fillingmaterial and suppressing configuration changes, such as horizontalfalls, etc. of the carbon nanotubes, so as to maintain the originalorientation of the carbon nanotubes (refer to the manufacturing methodto be described later).

The space of the region where each carbon nanotube bundle 12 is formedis not specifically limited, but for, e.g., the round region, thediameter can be set at, e.g., 10 μm-1000 mm.

The gap necessary between the carbon nanotube bundles 12 variesdepending on a viscosity of the filling material to be the filling layer16 and cannot be unconditionally determined but can be set at a widthsufficiently larger than a gap between the carbon nanotubes forming eachcarbon nanotube bundle 12, preferably at a value of about 0.1 μm-200 μm.However, as the gap between the carbon nanotube bundles 12 is larger,the surface density of the carbon nanotubes in the sheet surfacedecreases, that is, the thermal conductivity for the sheet decreases.The surface density of the carbon nanotubes in the sheet surface variesalso depending on a size of the carbon nanotube bundles 12. Accordingly,the gap between the carbon nanotube bundles may be suitably setcorresponding to a thermal conductivity necessary for the sheet and alsoin consideration of a size of the carbon nanotube bundles 12.

The plane shape of each carbon nanotube bundle 12 is not limited to thecircle illustrated in FIG. 1A and can be, other than a circle, apolygon, e.g., a triangle, a quadrangle, a hexagon or others.

The layout of a plurality of the carbon nanotube bundles 12 is notlimited to the close-packed arrangement of circle as shown in FIG. 1A.For example, as illustrated in FIGS. 2A and 2B, the carbon nanotubebundles 12 may be positioned respectively at the lattice points of asquare lattice. As illustrated in FIG. 2C, the carbon nanotube bundles12 of a triangular plane shape may be arranged in row, positionedalternately up-side-down. As illustrated in FIG. 2D, the carbon nanotubebundles 12 may be stripe-patterned. As illustrated in FIG. 2E, thecarbon nanotube bundles 12 may be comb-like patterned.

The graphite layer 14 is formed of graphite of the layer structureparallel with the surface of the sheet and is formed connected to theside surfaces of the carbon nanotube bundles 12. The thickness of thegraphite layer 14 is, e.g., about several nms-hundreds nms.

The material forming the filling layer 16 is not specifically limited aslong as the material has liquid properties in burying the carbonnanotubes and then can be cured. For example, as an organic fillingmaterial, acryl resin, epoxy regin, silicone resin, polyimide resin orothers can be used. As an inorganic filling material, a composition forforming insulating film by coating, such as SOG (Spin On Glass) orothers, or others can be used. A metal material, such as indium, solder,a metal paste (e.g., silver paste) or others can be also used. Aconductive polymer, e.g., polyaniline, polythiophene or others, can bealso used.

An additive may be mixed in the filling layer 16 as required. As anadditive, a material of high thermal conductivity or a material of highelectric conductivity are considered. An additive of high thermalconductivity is mixed in the filling layer 16, whereby the thermalconductivity of the filling layer 16 can be improved, which can improvethe thermal conductivity of the carbon nanotube sheet as a whole. Whenthe carbon nanotube sheet is used as an electric conductive sheet, anadditive of high electric conductivity is mixed in the filling layer 16,whereby the electric conductivity of the filling layer 16 can beimproved, which can improve the electric conductivity of the carbonnanotube sheet as a whole. The additive is especially effective when aninsulating material of low thermal conductivity, e.g., an organicfilling material or others, is used as the filling layer 16. As amaterial of high thermal conductivity, carbon nanotube, a metalmaterial, aluminum nitride, silica, alumina, graphite, fullerene orothers can be used. As a material of high electric conductivity, carbonnanotube, a metal material or others can be used.

As described above, the carbon nanotube sheet 10 according to thepresent embodiment includes the carbon nanotube bundles 12 orientedvertical to the surface of the sheet, and the graphite layer 14 ofgraphite of the layer structure parallel with the surface of the sheet.The carbon nanotube has a very high thermal conductivity of about 1500(W/m·K) in the direction of the orientation. The graphite has a thermalconductivity which is not so high as the thermal conductivity of thecarbon nanotube, but the thermal conductivity in the direction parallelto the layer surface (a-axis) is as high as about 500 (W/m·K).

Accordingly, as in the present embodiment, the carbon nanotube sheet 10comprises the combination of the carbon nanotube bundles 12 and thegraphite layer 14, whereby the thermal conductivity in the directionvertical to the surface of the sheet is ensured by the carbon nanotube(the carbon nanotube bundles 12), and the thermal conductivity in thedirection parallel to the surface of the sheet can be ensured by thegraphite (the graphite layer 14).

The thermal conductivity of graphite is 500 times or more the thermalconductivity of resinous materials (about 1 (W/m·K)). Accordingly, thepresence of the graphite layer 14 can drastically improve the radiationin the direction parallel to the surface of the sheet by 500 times ormore in comparison with the radiation without the graphite layer 14.

The carbon nanotube sheet 10 according to the present embodiment has theupper ends and lower ends of the carbon nanotube bundles 12 not coveredby the filling layer 16. Accordingly, when the carbon nanotube sheet 10comes into contact with a radiator or an exothermic body, the carbonnanotube bundles 12 in direct contact with the radiator or theexothermic body can drastically improve the thermal conductivity.

Carbon nanotube and graphite have also high conductivity, and the carbonnanotube bundles 12, which have the upper ends and lower ends exposed,can be used as interconnections passed through the sheet. The graphitelayer 14 can be used also as interconnections parallel to the surface ofthe sheet. That is, the carbon nanotube sheet 10 according to thepresent embodiment can be used not only as a thermal conductive sheetbut also as an interconnection sheet.

The relationship between the height of the carbon nanotube bundles 12and the thickness of the filling layer 16 (both are sheet thickness-wiselengths) can be that both are equal to each other as illustrated in FIG.3A, that one ends of the carbon nanotube bundles can be dented withrespect to the surface of the filling layer 16 as illustrated in FIG.3B, or that one ends of the carbon nanotubes 12 are projected withrespect to the surface of the filling layer 16. Such configurations canbe discriminately formed by changing the material and processingconditions of the filling layer 16 (see the manufacturing method to bedescried later).

The configuration illustrated in FIG. 3B is expected to mitigate thestresses to be applied to the carbon nanotube bundles 12 by the fillinglayer 16 when the carbon nanotube sheet 10 is arranged between aradiator and an exothermic body. On the other hand, the configurationillustrated in FIG. 3C is expected to improve the adhesion of the carbonnanotube bundles 12 to the radiator and the exothermic body and improvethe thermal conductivity. Preferably, the relationship between theheight of the carbon nanotube bundles 12 and the thickness of thefilling layer 16 are set suitably depending on applications of thecarbon nanotube sheet 10, stresses to be applied to the sheet, etc.

Next, the method of manufacturing the carbon nanotube sheet according tothe present embodiment will be described with reference to FIGS. 4 and5.

First, a substrate 30 to be used as a base for the carbon nanotube sheet10 to be formed on is prepared. As the substrate 30, a semiconductorsubstrate, such as a silicon substrate, an insulating substrate, such asan alumina (sapphire) substrate, an MgO substrate, a glass substrate orothers, can be used. The substrate 30 may be such substrate with a thinfilm formed on. For example, silicon substrate with an about 300nm-thickness silicon oxide film formed on can be used.

The substrate 30 is to be removed after the carbon nanotube sheet 10 isformed. For this purpose, it is preferable that the substrate 30 has atleast the surface to be contacted to the carbon nanotube sheet 10 formedof a material which is easy to be released from the carbon nanotubesheet 10 or a material which can be etched selectively with respect tothe carbon nanotube sheet 10.

For example, when the filling layer 16 is formed of acryl resin, amaterial whose adhesiveness to acryl resin is weak, e.g., silicon oxidefilm, silicon nitride film or others, is formed on the surface of thesubstrate 30, whereby the carbon nanotube sheet 10 can be easilyreleased. Otherwise, the surface of the substrate 30 is formed of amaterial which can be etched selectively with respect to the carbonnanotube sheet 10, e.g., silicon oxide film, silicon nitride film orothers, whereby the film is etched off to thereby release the carbonnanotube sheet 10 from the substrate 30.

Then, over the substrate 30, an about 0.3 nm-10 nm, e.g., a 2.5nm-thickness Fe (iron) film is formed by, e.g., sputtering method tothereby form a catalytic metal film 32 a of Fe (FIG. 4A). The catalyticmetal film 32 a may be formed by electron beam evaporation method, MBEmethod or others.

The catalytic metal can be, other than Fe, Co (cobalt), Ni (nickel), Au(gold), Ag (silver), Pt (platinum) or an alloy containing at least oneof these metals. As the catalyst, other than metal film, metalparticulates of a beforehand controlled size prepared by a DMA(differential mobility analyzer) or others may be used. In this case aswell, the metal species can be the same as the species for the thinfilm.

As a base film of the catalytic metal, a film of Mo (molybdenum), Ti(titanium), Hf (hafnium), Zr (zirconium), Nb (niobium), V (vanadium),TaN (tantalum nitride), TiSi_(x) (titanium silicide), Al (aluminum),Al₂O₃ (aluminum oxide), TiO_(x) (titanium oxide), Ta (tantalum), W(tungsten), Cu (copper), Au (gold), Pt (platinum), Pd (palladium), TiN(titanium nitride) or others, or a film of an alloy containing at leastone of them may be formed. For example, the layer structure of Fe (2.5nm)/Al (10 nm), the layer structure of Co (2.6 nm)/TiN (5 nm), or otherscan be also used. When the metal particulates are used, the layerstructure of, e.g., Co (the average diameter: 3.8 nm)/TiN (5 nm) orothers can be used.

Next, over the catalytic metal film 32 a, a photoresist film 34 isformed by spin coating method.

Next, in the photoresist film 34, openings 36 covering the regions forthe carbon nanotube bundles 12 to be formed on and exposing the regionfor the graphite layer 14 to be formed on are formed. As the pattern ofthe openings 36, the pattern exemplified in FIG. 1A is used, thediameter of the openings 36 (the diameter of the regions for the carbonnanotube bundles 12 to be formed in) is 100 μm, and the gap between theopenings 36 (between the carbon nanotube bundles 12) is 20 μm. As thepattern of the openings 36 to be formed in the photoresist film 34,other than the pattern exemplified in FIG. 1A, various patterns asillustrated in FIGS. 3A to 3E can be used.

Then, an Fe (iron) film of an about 10-200 nm-thickness, e.g., a 97.5 nmfilm thickness is formed by e.g., sputtering method to form thecatalytic metal film 32 b of Fe. The catalytic meal film 32 b is formedover the photoresist film 34 and the catalytic metal film 32 a in theopenings 36 a (FIG. 4B). As the constituent material of the catalyticmetal film 32 b, the same catalytic metal material of the catalyticmetal film 32 a is used. The catalytic metal film 32 b may be formed byelectron beam evaporation method, MBE method or others.

Next, the catalytic metal film 32 b is lifted off together with thephotoresist film 34 to leave the catalytic metal film 32 b selectivelyon the catalytic metal film 32 a. Thus, the catalytic metal film 32 a ofa 2.5 nm-thickness Fe film in the regions for the carbon nanotubebundles 12 to be formed in, and in the regions for the graphite layer 14to be formed in, the catalytic metal films 32 a, 32 b of a 100nm-thickness Fe film is formed (FIG. 4C).

Next, by, e.g., hot filament CVD method and with the catalytic metalfilms 32 a, 32 b as the catalyst, carbon nanotubes and graphite aregrown on the substrate 30 respectively in the regions for the carbonnanotube bundles 12 to be formed in and in the regions for the graphitelayer 14 to be formed in.

At this time, by suitably setting the film thicknesses and growthconditions of the catalytic metal films 32 a, 32 b, the carbon nanotubesand the graphite can be simultaneously grown.

In the regions where the catalytic metal film is thin (the regions forthe carbon nanotube bundles to be formed in), the catalytic metal isaggregated into particulates at a temperature of the growth. The growthadvances with the catalytic metal particles as the cores, and the carbonnanotubes are formed. On the other hand, in the regions where thecatalytic metal film is thick (the regions for the graphite layer 14 tobe formed in), the catalytic metal does not aggregate at the temperatureof the growth and remains in the films. Thus, with the catalytic metalfilms as the cores, the growth advances flat, and the graphite isformed.

Thus, in the regions for the carbon nanotube bundles to be formed in,the metal film of a film thickness which allows the catalytic metal toaggregate at the temperature of the growth is formed, and in the regionsfor the graphite layer to be formed in, the catalytic metal film of afilm thickness which does not allow the catalytic metal to aggregate atthe temperature of the growth.

In the above-described example, that the catalyst metal film of a 2.5nm-thickness Fe film is formed in the regions for the carbon nanotubebundles 12 to be formed in, and the catalyst metal films 32 a, 32 b of a100 nm-thickness Fe film is formed in the region for the graphite layer14 to be formed in, by using the mixed gas of acetylene and argon (thepartial pressure ratio of 1:9), and setting the total gas pressure inthe film forming chamber at 1 kPa, 620° C. temperature and the growthperiod of time at 20 minutes, multi-walled carbon nanotubes of a wallnumber of 3-6 walls (about 4 walls on average), a 4-8 nm (6 nm onaverage)-diameter, a 100 μm-length and an about 1×10¹¹ tubes/cm²-densitycould be grown, and in the region for the graphite layer 14 to be formedin, graphite of a 13 nm-thickness could be grown.

In the example using the above-described growth conditions, therelationships between the film thickness of the Fe film as the catalyticmetal film and the growths were examined, and the result is as follows.When the film thickness of the catalytic metal film is less than 10 nm,the carbon nanotubes were grown. When the film thickness of thecatalytic metal film is not less than 10 nm and less than 20 nm, boththe carbon nanotubes and the graphite were grown. When the filmthickness of the catalytic metal film is 20-1000 nm, the graphite wasgrown.

The catalytic metal more easily forms into particulates as thetemperature is higher. The conditions for forming the particulatesdiffer depending on species of the catalytic metal. Accordingly it ispreferable to suitably adjust the film thickness of the catalytic metalfilm depending on species of the catalytic metal, the growthtemperature, etc.

The carbon nanotubes and the graphite may be formed by another filmforming process, such as thermal CVD method or others. The carbonnanotubes to be grown may be single-walled carbon nanotubes. As thecarbon raw material, a hydrocarbon other than acetylene, such asmethane, ethylene or others, an alcohol, such as ethanol, methanol orothers, or others may be used.

Thus, over the substrate 30, carbon nanotube bundles including aplurality of carbon nanotubes oriented in the normal direction of thesubstrate 30 (vertically), and the graphite layer 14 of graphite of thelayer structure parallel with the surface of the sheet (FIG. 5A).

Then, a filling material to be the filling layer 16 is coated by, e.g.,spin coating method. At this time, the viscosity of the coating solutionand the rotation number of the spin coater are suitably set so that thefilling material cannot cover the carbon nanotube bundles 12.

For example, when acryl resin is used as the filling material, theheight of the carbon nanotube bundles 12 and the thickness of thefilling layer 16 can be made substantially equal to each other bycoating acryl resin of, e.g., a 440 mPa·s viscosity under the conditionsof 2000 rpm and 20 seconds.

The thickness of the filling layer 16 is made smaller than the height ofthe carbon nanotube bundles 12 by coating acryl resin of, e.g., a 440mPa·s viscosity under the conditions of 4000 rpm and 20 seconds andotherwise by coating acryl resin diluted to 80 w % with MEK (methylethyl ketone) solution under the conditions of 2000 rpm and 20 seconds.

It is possible to coat the filling material covering the carbon nanotubebundles 12 and then expose the upper surfaces of the carbon nanotubebundles 12 by plasma asking method, annealing method with oxygen orothers.

A metal thin film may be deposited over the carbon nanotube bundles 12and the graphite layer 14 before the filling material is coated. As themetal thin film, gold (Au) of, e.g., a 300 nm-thickness may bedeposited. The metal thin film is deposited over the carbon nanotubebundles, whereby the thermal resistance and the electric resistancebetween the carbon nanotubes can be decreased, and the eradiation of thecarbon nanotube sheet can be further improved.

The filling material is not specifically limited as long as the fillingmaterial exhibits liquid properties and then can be cured. For example,as an organic filling material, acryl resin, epoxy resin silicone resin,polyimide or others can be used. As an inorganic filling material, acomposition for forming insulating film by coating, such as SOG (Spin OnGlass) or others, or others can be used. A metal material, such asindium, solder, a metal paste (e.g., silver paste) or others can be alsoused. A conductive polymer, e.g., polyaniline, polythiophene or others,can be also used.

In forming the filling layer 16, because of the gaps between the pluralcarbon nanotube bundles 12 formed over the substrate 30, the coatingfilling material spreads over the entire surface of the substrate 30along the gaps. Then the filling material penetrates into the carbonnanotube bundles 12 and the graphite layer 14.

With carbon nanotubes formed over the entire surface of the substrate,when the filling material penetrates into the carbon nanotube bundles,individual carbon nanotubes adhere to one another, and the carbonnanotube bundles lose the original orientation and make configurationalchanges, such as horizontal falls.

However, gaps are provided between the carbon nanotube bundles 12 as inthe present embodiment, whereby the filling material spreads over theentire surface of the substrate 30 and the penetrates into the carbonnanotube bundles 12, whereby the filling material filled in advancebetween the carbon nanotube bundles 12 acts as the supporter forretaining the configuration of the carbon nanotubes when the fillingmaterial penetrates into the carbon nanotube bundles, and theconfigurational changes of the carbon nanotube bundles 12 can besuppressed. Thus, the filling layer can be formed with the orientationof the carbon nanotube bundles 12 retained.

The gap necessary between the carbon nanotube bundles 12 variesdepending on a species, viscosity, etc of the filling material andcannot be generally determined. However, the inventors of the presentapplication examined and have confirmed that the gap of not less than0.1 μm can prevent the configurational changes of the carbon nanotubebundles.

The filling layer 16 may be formed by immersing the substrate 30 in asolution of the filling material (the so-called dip method). In thiscase as well, the gap provided between the carbon nanotube bundles 12can prevent the configurational changes of the carbon nanotube bundles.

Next, the filling material is cured to form the filling layer 16 of thefilling material (FIG. 5B). For example, when a photo-cure material,such as acryl resin or others, is used as the filling material, thefilling material can be cured by photo irradiation. When a thermosettingmaterial, such as epoxy resin, silicone resin or others, is used as thefilling material, the filling material can be cured by heat processing.Epoxy resin can be thermoset by heat processing of, e.g., 150° C. and 1hour. Silicone resin can be thermoset by heat processing of, e.g., 200°C. and 1 hour.

After the filling layer 16 has been cured, when the upper ends of thecarbon nanotube bundles 12 are not sufficiently exposed or are coveredby the filling layer 16, the filling layer 16 over the carbon nanotubebundles 12 may be removed by CMP (chemical mechanical polishing), oxygenplasma asking, argon ion milling or others.

Then, the carbon nanotube bundles 12, the graphite layer 14 and thefilling layer 16 are peeled from the substrate 30, and the carbonnanotube sheet 10 is obtained (FIG. 5C).

At this time, when the surface of the substrate is formed of a materialwhich allows the carbon nanotube sheet 10 to be easily peeled from,e.g., when the surface of the substrate 30 is formed of silicon oxidefilm or silicon nitride film, and the filling layer is formed of acrylresin, the substrate 30 can be easily peeled form the carbon nanotubesheet 10.

Otherwise, when a layer which does not allow the carbon nanotube sheet10 to be easily peeled from but can be etched selectively with respectto the carbon nanotube sheet 10 is formed on the surface of thesubstrate 30, e.g., silicon oxide film or silicon nitride film is formedon the surface of the substrate 30, the silicon oxide film or thesilicon nitride film is removed by wet etching using a solution ofhydrofluoric acid or hot phosphoric acid or others to thereby free thecarbon nanotube sheet 10 from the substrate 30.

When the surface of the substrate 30 is formed of a material whichneither allows the carbon nanotube sheet 10 to be easily peeled form norcan be selectively removed, e.g., the substrate 30 is a sapphiresubstrate, and the filling layer 16 is formed of silicone resin, a sharpcutter is inserted between the substrate 30 and the carbon nanotubesheet 10 to thereby peel the carbon nanotube sheet 10 from the substrate30.

Before the peeling, the carbon nanotube bundles 12 and the graphitelayer 14 are in direct contact with the substrate 30, and on the surfaceof the peeled carbon nanotube sheet on the side of the substrate, thecarbon nanotube bundles 12 and the graphite layer 14 are exposed.Accordingly, in the carbon nanotube sheet 10 formed by theabove-described manufacturing method, the carbon nanotube bundles 12 canbe exposed on both surfaces of the sheet, and on one surface, thegraphite layer 14 can be exposed. At the parts where the carbon nanotubebundles 12 and the graphite layer 14 are exposed, connections can bemade with a metal such as In or others, a solder, a plating of, e.g.,AuSn, a metal paste, or others.

The thermal resistance of the conventionally used indium sheet is 0.21(° C./W) while the thermal resistance of the carbon nanotube sheetformed of only the carbon nanotubes formed by the above-describedprocess is 0.13 (° C./W). The thermal conductivity difference isreflected on the thermal resistance difference, and based on this, it isevident that the carbon nanotube sheet according to the presentembodiment, which includes in addition to the carbon nanotubes theexothermic graphite layer formed in parallel to the surface can morereduce the thermal resistance.

As described above, according to the present embodiment, a plurality ofthe carbon nanotube bundles are formed spaced from each other on asubstrate, and the filling layer for retaining the carbon nanotubebundles is formed by filling the filling material, wherebyconfigurational changes of the carbon nanotube bundles can be preventedin forming the filling layer. Thus, the carbon nanotube sheet includingthe carbon nanotube bundles oriented in the direction of the filmthickness of the sheet can be easily formed. Both ends of the carbonnanotube bundles can be exposed out of the filling layer, whereby thethermal conductivity and the electric conductivity to a connected bodycan be improved.

In the gaps between the carbon nanotube bundles, the graphite layer isformed in connection with the carbon nanotube bundles, whereby thethermal conductivity and the electric conductivity in the directionparallel with the sheet surface can be improved.

The carbon nanotube bundles and the graphite layer can be simultaneouslyformed, which makes it possible to form the carbon nanotube sheetwithout largely changing the manufacturing steps. Thus, themanufacturing cost increase can be prevented.

A Second Embodiment

A carbon nanotube sheet and a method of manufacturing the same accordingto a second embodiment will be described with reference to FIGS. 6A to9C. The same members of the present embodiment as those of the carbonnanotube sheet and the method of manufacturing the same according to thefirst embodiment illustrated in FIGS. 1A to 5C are represented by thesame reference numbers not to repeat or to simplify their explanation.

FIG. 6A is a plan view illustrating a structure of a carbon nanotubesheet according to the present embodiment. FIG. 6B is a diagrammaticcross-sectional view illustrating a structure of a carbon nanotube sheetaccording to the present embodiment. FIG. 7 is a diagrammaticcross-sectional view illustrating a structure of a carbon nanotube sheetaccording to a modification of the present embodiment. FIGS. 8A-9C arecross-sectional views illustrating a method of manufacturing the carbonnanotube sheet according to the present embodiment.

First, the structure of the carbon nanotube sheet according to thepresent embodiment will be described with reference to FIGS. 6A and 6B.FIGS. 6A and 6B are respectively a plan view and a cross-sectional viewillustrating the structure of the carbon nanotube sheet according to thepresent embodiment.

The carbon nanotube sheet 10 according to the present embodimentincludes a plurality of carbon nanotube bundles 12 arranged at a gapbetween each other (FIG. 6A). In the gaps between the carbon nanotubebundles 12, a carbon nanotube layer (a linear structure layer of carbonatoms) 18 having one ends on the surface of the sheet, a graphite layer20 formed on the carbon nanotube layer 18 and a filling layer 16 of aresinous material or others are buried (FIGS. 6A and 6B). The graphitelayer 20 is thermally and electrically connected to the carbon nanotubebundles 12 and the carbon nanotube layer 20.

In the present specification, the carbon nanotube bundles, the carbonnanotube layer, the graphite layer and the structure of them are oftencalled a carbon structure.

The carbon nanotube bundles 12 are formed extending vertically to thesurface of the sheet and each include a plurality of carbon nanotubesoriented vertically to the surface of the sheet.

The carbon nanotubes forming the carbon nanotube bundles 12 maysingle-walled carbon nanotubes or multi-walled carbon nanotubes. Thedensity of the carbon nanotubes contained in each carbon nanotubebundles 12 is preferably 1×10¹⁰ tubes/cm² or more in view of theradiation and electric conductivity. The length (the thickness of thesheet) of the carbon nanotube bundles 12 is determined by applicationsof the carbon nanotube sheet 10 and is not specifically limited.Preferably, the length can be set a value of about 5 μm-500 μm.

In the carbon nanotube sheet 10 according to the present embodiment,gaps are provided between the carbon nanotube bundles 12 over thegraphite layer 20, and the filling layer 16 is formed in the gaps. Thisis for improving the penetration of the filling material when thefilling layer 16 is formed between the carbon nanotubes and suppressingconfigurational changes, such as horizontal falls, etc., of the carbonnanotubes to thereby retain the original orientation of the carbonnanotubes (refer to the first embodiment).

The shape, the layout, etc. of the carbon nanotube bundles 12 are thesame as those of the first embodiment.

The carbon nanotube layer 18 is formed extended vertically to thesurface of the sheet and a plurality of carbon nanotubes orientedvertically to the surface of the sheet.

The carbon nanotubes forming the carbon nanotube layer 18 may besingle-walled carbon nanotubes or multi-walled carbon nanotubes. Thedensity of the carbon nanotubes contained in the carbon nanotube layer18 is preferably 1×10¹⁰ tubes/cm² or more in view of the radiation andelectric conductivity. The length (the thickness of the sheet) of thecarbon nanotube bundles 12 is determined by applications of the carbonnanotube layer 18 and is not specifically limited. Preferably, thelength can be set a value of about 5 μm-500 μm.

The graphite layer 20 is formed of graphite of the layer structureparallel with the surface of the sheet and formed in contact with theside surfaces of the carbon nanotube bundles 12 and the upper surface ofthe carbon nanotube layer 18. The thickness of the graphite layer 20 is,e.g., several nm-tens nm.

The constituent material of the filling layer 16 is the same as that ofthe first embodiment.

As described above, the carbon nanotube sheet 10 according to thepresent embodiment includes the carbon nanotube bundles 12 and thecarbon nanotube layer 18 oriented vertically to the surface of thesheet, and the graphite layer 20 of graphite of the layer structureparallel with the surface of the sheet. Carbon nanotube has a very highthermal conductivity of about 1500 (W/m·K) in the orientation direction.Graphite does not have so high a thermal conductivity as carbonnanotubes but the thermal conductivity in the direction parallel(a-axis) to the layer surface is 500 (W/m·K), which is very high.

Accordingly, as in the present embodiment, the carbon nanotube sheet 10includes the combination of the carbon nanotube bundles 12, the carbonnanotube layer 18 and the graphite layer 20, whereby the thermalconductivity in the direction vertical to the surface of the sheet isensured mainly by carbon nanotubes (the carbon nanotube bundles 12 andthe carbon nanotube layer 18), and the thermal conductivity in thedirection parallel to the surface of the sheet can be ensured by mainlyby graphite (the graphite layer 20).

Graphite has a thermal conductivity 500 times or more that of resinousmaterials (thermal conductivity: about 1 (W/m·K). By providing thegraphite layer 20, the radiation in the direction parallel to thesurface of the sheet can be improved drastically by 500 times or more incomparison with that without the graphite layer 20.

A point of the carbon nanotube sheet according to the present embodimentsuperior to the carbon nanotube sheet according to the first embodimentis that the graphite layer 20 is indirect contact with an exothermicbody to be provided below the carbon nanotube sheet with the carbonnanotube layer 18 provided therebetween. That is, in the carbon nanotubesheet according to the present embodiment, radiation is made to thegraphite layer 20 once via the carbon nanotube layer 18 is superior inthe radiation in the parallel direction to that of the carbon nanotubesheet according to the first embodiment, in which a radiator and thegraphite layer 20 are in direct contact with each other, especially whenthe contact area between the radiator and the sheet is substantially thesame as that of the sheet.

Furthermore, the carbon nanotube sheet 20 according to the presentembodiment has the upper ends and the lower ends of the carbon nanotubebundles 12 not covered by the filling layer 16. Thus, when the carbonnanotube sheet 20 is brought in contact with a radiator or an exothermicbody, the carbon nanotube bundles 12 are contacted with the radiator orthe exothermic body, and the thermal conductivity can be drasticallyincreased.

Because of the high electric conductivities of carbon nanotube andgraphite, with the upper ends and the lower ends of the carbon nanotubebundles 12 exposed, the carbon nanotube bundles 12 can be also used asinterconnections passed through the sheet. The graphite layer 20 canalso used as interconnections parallel with the surface of the sheet.That is, the carbon nanotube sheet 10 according to the presentembodiment is applicable not only as thermal conduction sheet but alsoas interconnection sheet.

The height of the carbon nanotube bundles 12 and the thickness of thefilling layer 16 (both are lengths in the direction of the thickness ofthe sheet) is the same as that of the first embodiment.

The carbon nanotube layer 18 and the graphite layer 20 to be formedbetween the carbon nanotube bundles 12 may be repeatedly stacked asexemplified in FIG. 7. In the example illustrated in FIG. 7, the carbonnanotube layer 18 and the graphite layer 20 are stacked in the 2-layerstructure but may be stacked in 3 or more layers.

The graphite layer 20 is provided in plural layers, whereby thesubstantial film thickness of the graphite layer 20 is increased, andthe thermal conductivity and the electric conductivity in the transversedirection can be improved.

Next, the method of manufacturing the carbon nanotube sheet according tothe present embodiment will be described with reference to FIGS. 8 and9.

First, a substrate 30 to be used as the base for forming the carbonnanotube sheet 10 is prepared. As the substrate 30, various substratesdescribed in the first embodiment can be used.

Then, over the substrate 30, a photoresist film (not illustrated) forexposing regions for the carbon nanotube bundles 12 to be formed in isformed by the photolithography. The shape and the layout of the regionfor the carbon nanotube bundles 12 to be formed in are the same as thoseof the first embodiment. The regions for the carbon nanotube bundles 12to be formed in are the circle of, e.g., a 100 μm-diameter, and the gapbetween the adjacent regions is, e.g., 100 μm.

Then, an Fe film of, e.g., a 2.5 nm-thickness is deposited by, e.g.,sputtering method to form a catalytic metal film 32 of Fe film. As thecatalytic metal, the same catalytic metal material as in the firstembodiment can be used.

Then, the catalytic metal film 32 on the photoresist film is lifted offtogether with the photoresist film to leave the catalytic metal film 32selectively in the regions for the carbon nanotube bundles 12 to beformed in. Thus, in the regions for the carbon nanotube bundles 12 to beformed in, the catalytic metal film 32 of Fe film of, e.g., a 2.5nm-thickness is formed (FIG. 8A).

Then, over the substrate 30, carbon nanotubes are grown by, e.g., hotfilament CVD method with the catalytic metal film 32 as the catalyst.The growth conditions for the carbon nanotubes are, e.g., the mixed gasof acetylene and argon (partial pressure ratio of 1:9) as the rawmaterial gas, 1 kPa of the total gas pressure in the film formingchamber, 620° C. temperature and 20 minutes of growth period time. Underthese conditions, multi-walled carbon nanotubes of a wall number of 3-6walls (about 4 walls on the average), a 4-8 nm (6 nm on the average)diameter and a 100 μm-length can be grown. The carbon nanotubes may beformed by another growth method, such as thermal CVD method, remoteplasma CVD method or others. The carbon nanotubes to be grown may besingle-walled carbon nanotubes. As the carbon raw material, other thanacetylene, hydrocarbon, such as methane, ethylene or others, an alcohol,such as ethanol, methanol or others, or others may be used.

Thus, over the substrate 30 in the regions for the catalytic metal film32 formed in, carbon nanotube bundles 12 having a plurality of carbonnanotubes oriented in the normal direction of the substrate 30 areselectively formed (FIG. 8B). The carbon nanotube bundles formed underthe above-described growth conditions each had an about 1×10¹¹ tubes/cm²carbon nanotube density.

Then, over the substrate 30 with the carbon nanotube bundles 12 formedon, a TiN film of, e.g., a 5 nm-thickness and a Co film of, e.g., a 2.6nm-thickness are sequentially deposited by, e.g., sputtering method toform a catalytic metal film 38 of the Co/TiN layer structure (FIG. 8C).At this time, because of the upper ends of the carbon nanotube bundles12, which do not form a continuous flat surface, the catalytic metalfilm 38 is not formed in a film on the carbon nanotube bundles 12. Asthe base film of the catalytic metal film 38, other than TiN, anothermaterial containing Ti, e.g., Ti (titanium), TiO₂ (titanium oxide) orothers can be used.

Next, over the substrate 30, by, e.g., thermal CVD method with thecatalytic metal film 38 as the catalyst, the carbon nanotube layer 18having the upper surface coated by the graphite layer 20 is formed (FIG.9A).

The carbon nanotube layer 18 having the upper surface coated by thegraphite layer 20 can be grown by using the raw material gas ofhydrocarbon, such as acetylene, methane, ethylene or others at arelatively low temperature of about 450° C.-510° C. For example, the rawmaterial gas is the mixed gas of acetylene and argon (the partialpressure ratio of 1:9), 1 kPa of the total gas pressure in the filmforming chamber, 450° C.-510° C. temperature and 30 minutes of growthperiod of time. Thus, the carbon nanotube layer 18 of multi-walledcarbon nanotubes of a wall number of 3-6 walls (about 4 walls on theaverage), a 4-8 nm diameter (6 nm on the average) and a 20 μm-length canbe grown. On the carbon nanotube layer 18, the graphite layer 20 of 18nm-thickness is formed.

The carbon nanotube layer 18 having the upper surface coated by thegraphite layer 20 can be formed by suitably controlling the filmthickness of the catalytic metal film 38 (the film thickness of Co film)and the film forming temperature.

Table 1 represents the result of the examined relationships between thefilm thickness of the Co film of the catalytic metal film 38 and thefilm forming temperature, and the fabricated structure. The filmthickness of the TiN film forming the catalytic metal film 38 wasconstantly 5 nm.

TABLE 1 Growth Temperature Co Film Thickness [nm] [° C.] 1.2 2.1 2.6 3.65 450 CNT Graphite/ Graphite/ Graphite/ — CNT CNT CNT 510 CNT Graphite/Graphite/ Graphite/ — CNT CNT CNT 590 CNT CNT CNT CNT CNT

In Table 1, “CNT” indicates the carbon nanotube layer formed of thecarbon nanotubes alone, and “Graphite/CNT” indicates the carbon nanotubelayer formed of the carbon nanotubes and having the upper surface coatedby the graphite layer.

As shown in Table 1, by setting the film thickness of the Co film at2.1-4.6 nm and the film forming temperature at 450° C.-510° C., thecarbon nanotube layer having the upper surface coated by the graphitelayer could be formed. The inventors of the present applicationspecifically examined and have found that the carbon nanotube layerhaving the upper surface coated by the graphite layer can be formed bythe growth with the film thickness of the Co film set at 2.0 nm-7.0 nmand the film forming temperature set at 350° C.-560° C.

The thickness of the graphite layer to be formed can be controlled bythe film thickness of the Co film and the film forming temperature. Whenthe temperature was 510° C., the graphite layer of a 4 nm-thicknesscould be formed with the film thickness of the Co film set at 2.1 nm;with the film thickness of the Co film set at 2.6 nm, the graphite layerof a 18 nm-thickness graphite layer could be formed; and with the filmthickness of the Co film set at 3.6 nm, the graphite layer of a 30nm-thickness could be formed. When the film forming temperature was 450°C., the graphite layer of a 20 nm-thickness could be formed with thefilm thickness of the Co film set at 3.6 nm.

The mechanism of the carbon nanotube layer 18 having the upper surfacecoated by the graphite layer 20 being formed is not clear, but theinventors of the present application presume as follows.

In the present embodiment, the carbon nanotube layer 18 is grown at alower temperature than the carbon nanotube bundles 12. Accordingly, atthe initial stage of the growth, the Co film of the catalytic metal filmis not sufficiently aggregated, and graphite will be grown homogeneouslyover the catalytic metal film 38. Then, as the Co film aggregates, thegrowth of the carbon nanotubes will start, and resultantly, the carbonnanotube layer 18 having the upper surface coated by the graphite layer20 will be formed.

When the carbon nanotube layer 18 having the upper surface coated by thegraphite layer 20 is grown, the graphite layer 20 is formed in about 1second on the initial stage of the growth. The thickness of the carbonnanotube layer 18 (the length of the carbon nanotubes) can bearbitrarily controlled by the growth period of time.

Then, in forming the carbon nanotube sheet of the structure illustratedin FIG. 7, the above-described steps illustrated in FIG. 8C to FIG. 9Aare repeated as required to thereby stack the layer body of the carbonnanotube layer 18 and the graphite layer 20 by a prescribed layernumber.

The upper surface of the graphite layer 20, which is formed plane, as isnot the upper surfaces of the carbon nanotube bundles 12, allows thecatalytic meal film 38 to be deposited thereon. Thus, the carbonnanotube layer 18 and the graphite layer 20 can be repeated grown.

Then, in the same way as in the method of manufacturing the carbonnanotube sheet according to the first embodiment, the filling layer 16formed buried in the regions between the carbon nanotube bundles 12,between the carbon nanotubes and in the graphite layer (FIG. 9B).

Next, in the same way as in the method of manufacturing the carbonnanotube sheet according to the first embodiment, the carbon nanotubebundles 12, the carbon nanotube layer 18, the graphite layer 20 and thefilling layer 16 are peeled from the substrate 30, and the carbonnanotube sheet 10 is obtained (FIG. 9C).

As described above, according to the present embodiment, a plurality ofcarbon nanotube bundles are formed over the substrate, spaced from eachother, and then the filling material is filled to form the filling layerfor retaining the carbon nanotube bundles, whereby the configurationalchanges of the carbon nanotube bundles in forming the filling layer canbe prevented. Thus, the carbon nanotube sheet including the carbonnanotube bundles oriented in the direction of the film thickness of thesheet can be easily formed. Both ends of the carbon nanotube bundles canbe exposed out of the filling layer, whereby the thermal conductivityand the electric conductivity to a connected body can be improved.

In the gaps between the carbon nanotube bundles, the layer body of thecarbon nanotube layer and the graphite layer is formed in contact withthe carbon nanotube bundles, whereby the thermal conductivity and theelectric conductivity in the direction parallel to the sheet surface canbe improved.

A Third Embodiment

A semiconductor device and a method of manufacturing the same accordingto a third embodiment will be described with reference to FIGS. 10 to13C.

FIG. 10 is a diagrammatic cross-sectional view illustrating a structureof a semiconductor device according to the present embodiment. FIGS.11A-13C are cross-sectional views illustrating a method of manufacturingthe semiconductor device according to the present embodiment.

First, the structure of the semiconductor device according to thepresent embodiment will be described with reference to FIG. 10.

An interconnection layer 42 is formed over a substrate 40. Over thesubstrate 40 in the region except the region where the interconnectionlayer 42 is formed, an inter-layer insulating film 44 is formed. Overone end of the interconnection layer 42, a via interconnection 64 of acarbon nanotube bundle is formed with a TiN film 50 interposedtherebetween. Over the via interconnection 64, an interconnection layer66 of graphite is formed in connection with the via interconnection 64.Over the interconnection layer 42 and the inter-layer insulating film 44in the region where the interconnection layer 66 is formed except theregion where the via interconnection 64 is formed, a TiO₂ film 56 isformed. Around the via interconnection 64 and the interconnection layer66, an inter-layer insulating film 68 is formed. Over one end of theinterconnection layer 66, a via interconnection 72 of a carbon nanotubebundle is formed with a TiN film 70 interposed therebetween. Over thevia interconnection 72, an interconnection layer 74 of graphite isformed in connection with the via interconnection 72. Over theinter-layer insulating film 68 in the region where the interconnectionlayer 74 is formed except the region where the via interconnection 72 isformed, a TiO₂ film is formed. Around the via interconnection 72 and theinterconnection layer 74, an inter-layer insulating film 76 is formed.

As described above, in the semiconductor device according to the presentembodiment, the via interconnection (e.g., the via interconnection 64)interconnecting the lower interconnection layer (e.g., theinterconnection layer 42) and the upper interconnection (e.g., theinterconnection layer 66) is formed of the carbon nanotube bundles. Theinterconnection layer (e.g., the interconnection layer 66) connected tothe via interconnection of carbon nanotube bundles (e.g., the viainterconnection 64) is formed of the graphite layer.

The interconnection layers and the via interconnections are formed ofgraphite and carbon nanotubes of low resistance values, whereby theinterconnection resistance can be drastically decreased. Thus, thehigh-speed operation of the semiconductor device is made possible, andthe electric power consumption can be decreased.

Next, the method of manufacturing the semiconductor device according tothe present embodiment will be described with reference to FIGS. 11 to13.

Over the substrate 40, the interconnection layer and the inter-layerinsulating film 44 have been formed (FIG. 11A). The interconnectionlayer 42 and the inter-layer insulating film 44 have been formed by theordinary semiconductor device manufacturing process. The substrate 40includes not only semiconductor substrates themselves, such as siliconsubstrates, etc. but also semiconductor substrates with elements, suchas transistors, etc., interconnection layers of 1 layer, or or morelayers formed on. As the material of the interconnection layer 42,copper, for example, can be used. In this case, over the bottom of thevia, tantalum or others for preventing the diffusion of copper isdeposited.

Over the substrate 40, a photoresist film 48 exposing the region wherethe via portion for connecting the upper interconnection layers to theinterconnection layer 42 is to be formed and covering the rest region isformed by photolithography.

Then, by, e.g., sputtering method, the TiN film of an about 1-20nm-thickness, e.g., a 5 nm-thickness, and a Co film of an about 2-3nm-thickness, e.g., a 2.1 nm-thickness are sequentially deposited toform a catalytic metal film of the Co/TiN layer structure (FIG. 11B).The catalytic metal film may be formed by electron beam evaporationmethod, CVD method, MBE method or others.

In place of selectively forming the catalytic metal film by lift offmethod as described above, the catalytic metal film may be formed overthe entire surface and patterned by photolithography or ion milling. Thepatterning method can be EB (Electron Beam) exposure or others but isnot specifically limited.

Then, the TiN film 50 and the Co film 52 on the photoresist film 48 arelifted off together with the photoresist film 48 to leave the catalyticmetal film of the layer structure of the Co film 52/the TiN film 50selectively in the region for the via portion to be formed in (FIG.11C).

Next, by photolithography, a photoresist film 54 exposing the region forthe upper interconnection layer to be connected to the interconnectionlayer 42 is to be formed and which is the region except the region wherethe via portion where the catalytic metal film of the Co film 52/TiNfilm 50 is formed, and covering the reset region is formed.

Then, by, e.g., sputtering method, a TiO₂ film of an about 1-20nm-thickness, e.g., a 5 nm-thickness and a Co film of an about 3-7nm-thickness, e.g., a 4.5 nm-thickness is sequentially deposited to forma catalytic metal film of the Co/TiO₂ layer structure (FIG. 12A)

As the base film of the catalytic metal film to be formed in theinterconnection layer forming region except the via portion formingregion, the TiO₂ film 56, which is different from the TiN film 50 usedin the via portion forming region because the base film (TiN film 50 andthe TiO₂ film 56) of the catalytic metal film remain after theinterconnection layer has been formed. That is, this is because in thevia portion forming region, the TiN film 50, which is electricconductive, is used so as to ensure the electric connection with thebase interconnection layer 42, but if an electric conductive film, suchas TiN film, is formed also in the interconnection layer forming regionexcept the via portion forming region, there is a risk of short circuitswith other interconnection layers via the TiN film 50. From such viewpoint, it is preferable that in the interconnection layer forming regionexcept the via portion forming region, an insulative base film of TiO₂film or others is formed. When there is no risk of short circuitsbetween the interconnection layers, an electric conductive base film maybe used, as is in the via portion forming region.

Then, the TiO₂ film 56 and the Co film 58 on the photoresist film 54 arelifted off together with the photoresist film 54 to leave the catalyticmetal film of the layer structure of the Co film 58/the TiO₂ film 56selectively in the interconnection layer forming region except the viaportion forming region (FIG. 12B).

Next, by, e.g., thermal CVD method, with the catalytic metal film as thecatalyst, the carbon nanotubes and the graphite are grown. The growthconditions for this are, e.g., the mixed gas of acetylene and argon (thepartial pressure ratio of 1:9) as the raw material gas, 1 kPa of thetotal gas pressure in the film forming chamber and 450° C. temperature,whereby in the via portion forming region, where the catalytic film ofthe Co film 52/the TiN film 50 is formed, the via interconnection 64 ofthe carbon nanotube bundle is formed, and in the interconnection layerforming region, where the Co film 58/the TiO₂ film 56 is formed, theinterconnection layer 66 of the graphite layer extended over the viainterconnection 64 is formed, spaced from the TiO₂ film 56 (FIG. 12C).The carbon nanotubes and the graphite may be formed by hot filament CVDmethod, remote plasma CVD method or others.

The Co films 52, 58 are formed into particulates in the process ofgrowing the carbon nanotubes and the graphite and taken into the carbonnanotubes or the graphite.

The structures formed respectively over the catalytic metal film of theCo film 52/TiN film 50 and over the catalytic metal film of the Co film58/the TiO₂ film 56 are different from each other under the influence ofthe different growth rates due to the film thickness difference betweenthe Co films.

The conditions for the growth with the Co film of a 2.1 nm-thickness anda 4.5 nm-thickness as the catalyst at the above film forming temperatureare the conditions for growing the carbon nanotubes having the uppersurfaces coated by the graphite layer, as described in the secondembodiment. However, the growth rate of the carbon nanotubes in theregion where the 4.5 nm-thickness Co film is formed is much lower thanthe growth rate of the carbon nanotubes in the region where the 2.1nm-thickness Co film is formed, and after the interconnection layer 66of the graphite layer has been formed, the growth of the carbonnanotubes over the catalytic metal film of the Co film 52/TiN film 50 isdominant. Resultantly, as the carbon nanotubes grow onto the catalyticmetal film of the Co film 52/the TiN film 50, the entire graphite layerin the interconnection layer forming region is lifted, and the carbonnanotubes do not grow onto the catalytic film of the Co film 58/the TiO₂film 56. Resultantly, the via interconnection 64 and the interconnectionlayer 66 as illustrated in FIG. 12C are formed.

Table 2 represents the lengths of the carbon nanotubes formed when theCo film thickness and the growing conditions of the carbon nanotubes arevaried.

TABLE 2 Co Film Thickness Growth Conditions [nm] 450° C. 60 min 510° C.10 min 2.1 — 7.0 μm 2.6 0.8 μm 5.0 μm 3.6 0.6 μm 3.0 μm 4.5 0.3 μm 0.4μm

As shown in Table 2, the growth rate of the carbon nanotubes lowers atall the growth temperatures as the film thickness of the Co film isthicker. Accordingly, the film thickness of the Co film to be depositedin the via interconnection forming region and the interconnection layerforming region are suitably set, whereby the via interconnection of thecarbon nanotube bundle and the interconnection layer of the graphitelayer can be simultaneously formed.

Next, over the substrate 40 with the interconnection layer 66 formed,the inter-layer insulating film 68 coating the interconnection layer 66is formed by e.g., spin coating method or CVD method (FIG. 13A).

Then, the surface of the inter-layer insulating film 68 is polished by,e.g., CMP method until the surface of the interconnection layer 66 isexposed (FIG. 13B).

Next, the steps illustrated in FIG. 11B to FIG. 13A are repeated asrequired to thereby form over the interconnection layer 66, a viainterconnection 72 electrically connected to the interconnection layer66 via a TiN film 70, an interconnection layer 74, an inter-layerinsulating film 76, etc. (FIG. 13C).

As described above, according to the present embodiment, the viainterconnection formed of the carbon nanotube bundle, and theinterconnection layer formed of the graphite layer connected to the viainterconnection can be formed, whereby the electric resistance of thevia interconnection and the interconnection layer can be drasticallydecreased, and the characteristics of the semiconductor device can beimproved. The via interconnection of the carbon nanotube bundle and theinterconnection layer of the graphite layer can be simultaneouslyformed, whereby an interconnection structure can be formed withoutlargely changing manufacturing steps, and the manufacturing costincrease can be prevented.

A Fourth Embodiment

A semiconductor device and a method of manufacturing the same accordingto a fourth embodiment will be described with reference to FIGS. 14 to17C.

FIG. 14 is a diagrammatic cross-sectional view illustrating a structureof a semiconductor device according to the present embodiment. FIGS.15A-17C are cross-sectional views illustrating a method of manufacturingthe semiconductor device according to the present embodiment.

First, the structure of the semiconductor device according to thepresent embodiment will be described with reference to FIG. 14.

An interconnection layer 42 is formed over a substrate 40. Over thesubstrate 40 with the interconnection layer 42 formed, an inter-layerinsulating film 44 is formed. In the inter-layer insulating film 44,contact holes 46 down to the interconnection layer 42 are formed. Overthe interconnection layer 42 in the contact holes 46, viainterconnections 64 of carbon nanotube bundles are formed with a TiNfilm interposed therebetween. Over the via interconnections 64, aninterconnection layer 84 connected to the via interconnections 64 isformed. The interconnection layer 84 includes a graphite layer 66 aformed over the via interconnections 64, a graphite layer 66 b formedover the inter-layer insulating film with a TiN film 66 interposedtherebetween and a TiC film 82 formed over the graphite layers 66 a, 66b.

As described above, in the semiconductor device according to the presentembodiment, the via interconnection (e.g., the via interconnections 64)interconnecting a lower interconnection (e.g., the interconnection layer42) and an upper interconnection (e.g., the interconnection layer 84) isformed of carbon nanotube bundles. An interconnection layer (e.g., theinterconnection layer 84) connected to the via interconnection (e.g.,the interconnections 64) formed of carbon nanotube bundles is formed ofthe graphite layers 66 a, 66 b and the TiC film 82.

The interconnection layer and the via interconnections are formed ofgraphite and carbon nanotube whose resistance value are low, whereby theinterconnection resistance can be drastically decreased. This makes thehigh-speed operation of the semiconductor device possible, and theelectric power consumption can be decreased.

The TiC film formed on the graphite layers 66 a, 66 b ensures theelectric connection between the graphite layers 66 a, 66 b. The TiC film82 is formed in consideration that the graphite layer 66 a and thegraphite layer 66 b are grown independently from different bases and,although formed in the adjacent regions, might not ensure sufficientelectric connection. If the electric connection between the graphitelayer 66 a and the graphite layer 66 b is sufficient, the TiC film 82may not be essentially formed.

Next, the method of manufacturing the semiconductor device according tothe present embodiment will be described with reference to FIGS. 15 to17.

The interconnection layer 42, and the inter-layer insulating film 44coating the interconnection layer 42 are formed over the substrate 40(FIG. 15A). The substrate 40 includes not only semiconductor substratesthemselves, such as silicon substrates or others, but also substrateswith elements, such as transistors, etc., interconnection layers of 1layer, or 2 or more layers formed on.

Next, by photolithography and dry etching, in the inter-layer insulatingfilm 44, the contact holes 46 down to the interconnection layer 42 areformed (FIG. 15B).

Next, by photolithography, over the inter-layer insulating film 44, aphotoresist film 48 exposing the regions where the contact holes 46 areto be formed and coating the rest region is formed. As the photoresistfilm 48, the photoresist film used in forming the contact holes 46 maybe used.

Then, by, e.g., sputtering method, the TiN film of an about 1-20nm-thickness, e.g., a 5 nm-thickness and a Co film 52 of an about 2-3nm-thickness, e.g., a 2.6 nm-thickness are sequentially deposited toform a catalytic metal film of the layer structure of Co/TiN (FIG. 11C).The catalytic metal film may be formed by electron beam evaporationmethod, CVD method, MBE method or others.

Then, the TiN film 50 and the Co film 52 on the photoresist film 48 arelifted off together with the photoresist film 48 to leave the catalyticmetal film of the layer structure of the Co film 52/the TiN film 50selectively on the interconnection layer 42 in the contact holes 46(FIG. 16A).

Next, by photolithography, a photoresist film 54 exposing the regionwhere the upper interconnection layer to be connected to theinterconnection layer 42 is to be formed and which is the region exceptthe region where the contact holes 46 are formed, and covering the restregion is formed.

Next, by, e.g., sputtering method, the TiN film of an about 1-20nm-thickness, e.g., a 5 nm-thickness, and the Co film 62 of an about 3-7nm-thickness, e.g., a 4.5 nm-thickness are sequentially deposited toform the catalytic metal film of the layer structure of Co/TiN (FIG.16B).

Then, the TiN film 60 and the Co film 62 on the photoresist film 54 arelifted off together with the photoresist film 54 to leave the catalyticmetal film of the layer structure of the Co film 62/the TiN film 60selectively in the region where the interconnection layer is to beformed and which is the region except the region where the contact holes46 are formed (FIG. 16C).

Next, by, e.g., thermal CVD method, with the catalytic metal film as thecatalyst, carbon nanotubes and graphite are grown. The conditions forthis growth are set at, e.g., the mixed gas of acetylene and argon gas(partial pressure ratio of 1:9) as the raw material gas, 1 kPa of thetotal gas pressure in the film forming chamber and 450° C. temperature,whereby the via interconnections 64 of carbon nanotube bundles havingthe upper surfaces coated by the graphite layer 66 a in the via portionforming region, where the Co film 52/the TiN film 50 is formed, and thegraphite layer 66 b in the interconnection layer forming region, wherethe Co film 62/the TiN film 60 is formed (FIG. 17A). The carbonnanotubes and the graphite may be formed by hot filament CVD method,remote plasma CVD method or others.

The Co films 52, 62 are formed into particulates in the process ofgrowing the graphite and are taken into the carbon nanotubes or thegraphite.

The structures formed respectively on the catalytic metal film of the Cofilm 52/the TiN film 50 and on the catalytic metal film of the Co film62/the TiN film 60 are different from each other, and this is influencedby the difference of the growth rate due to the difference of the filmthickness of the Co films.

The conditions for the growth with the 2.6 nm-thickness Co film and the4.5 nm-thickness Co film at the above-described film forming temperatureare both the conditions for the carbon nanotubes having the uppersurfaces coated by the graphite layer, as described in the secondembodiment. However, the growth rate of the carbon nanotubes in theregions with the 4.5 nm-thickness Co film formed in is much lower thanthe growth rate of the carbon nanotubes in the region with the 2.6nm-thickness Co film formed in, whereby the via interconnection 64 ofcarbon nanotube bundles are being formed below the graphite layer 66 a,the carbon nanotube bundles are not substantially grown below thegraphite layer 66 b. Resultantly, the via interconnection 64 and thegraphite layer 66 a, 66 b as illustrated in FIG. 17A are formed.

Next, by photolithography, a photoresist film 78 exposing theinterconnection layer forming region (the region where the graphitelayers 66 a, 66 b are formed) and covering the reset region is formed.

Next, a Ti film 80 of, e.g., a 50 nm-thickness is deposited by, e.g.,sputtering method (FIG. 17B).

Next, the Ti film 80 on the photoresist film 78 is lifted off togetherwith the photoresist film 78 to leave the Ti film 80 selectively on thegraphite layers 66 a, 66 b in the interconnection layer forming region.

Then, thermal processing of, e.g., 450° C. and 10 minutes is made toreact the Ti film 80 with the upper parts of the graphite layers 66 a,66 b to form a TiC (titanium carbide) film 82 on the surfaces of thegraphite layers 66 a, 66 b. TiC can be formed by only deposition bysputtering method, but this thermal processing advances the formation ofTiC. Thus, the interconnection layer 84 of the graphite layers 66 a, 66b and the TiC film 82 is formed (FIG. 17C).

As described above, according to the present embodiment, the viainterconnection of the carbon nanotube bundles, and the interconnectionlayer of the graphite layer connected to the via interconnection can beformed, whereby the electric resistance of the via interconnection andthe interconnection layer can be drastically decreased, and thecharacteristics of the semiconductor device can be improved. The viainterconnection of the carbon nanotube bundles and the interconnectionlayer of the graphite layer can be simultaneously formed, whereby theinterconnection structure can be formed without largely changing themanufacturing steps. This can prevent the manufacturing cost increase.

A Fifth Embodiment

An electronic device according to a fifth embodiment will be describedwith reference to FIG. 18.

FIG. 18 is a diagrammatic cross-sectional view illustrating thestructure of the electronic device according to the present embodiment.

In the present embodiment, the electronic device using the carbonnanotube sheet according to the first or the second embodiment as thethermal conductive sheet will be described.

Over a circuit board 100, such as a multi-level interconnectionsubstrate or others, a semiconductor element 106, e.g., a CPU, etc. aremounted. The semiconductor element 106 is electrically connected to thecircuit board 100 via solder bumps 102, and an under fill 104 is filledbetween the circuit board 100 and the semiconductor element 106.

Over the semiconductor element 106, a heat spreader 110 for diffusingthe heat from the semiconductor element 106 is formed covering thesemiconductor element 106. Between the semiconductor element 106 and theheat spreader 110, the carbon nanotube sheet 108 according to the firstor the second embodiment is formed. The carbon nanotube sheet 108 isarranged with the graphite layer 14 or the carbon nanotube layer 18positioned on the side of the semiconductor element 106, which is theexothermic source (refer to FIGS. 1 and 6).

Over the heat spreader 110, a heat sink 114 for radiating the heatconducted to the heat spreader 110 is formed. Between the heat spreader110 and the heat sink 114, the carbon nanotube sheet 112 according tothe first or the second embodiment is formed.

As described above, in the electronic device according to the presentembodiment, between the semiconductor element 106 and the heat spreader110 and between the heat spreader 110 and the heat sink 114, i.e., theexothermic units and the radiation units, the carbon nanotube sheets106, 112 according to the first or the second embodiment is respectivelyprovided.

As described above, the carbon nanotube sheet according to the first orthe second embodiment includes the carbon nanotube bundles 12 orientedvertical of the surface of the sheet, and the graphite layer 14 ofgraphite in the layer structure parallel with the film surface of thesheet, and has very high thermal conductivity in the directions normaland parallel to the surface.

Thus, the carbon nanotube sheet according to the first or the secondembodiment is used as the thermal conductive sheets formed between thesemiconductor element 106 and the heat spreader 110 and between the heatspreader 110 and the heat sink 114, whereby the heat emitted from thesemiconductor element 106 can be conducted vertically to the heatspreader 110 and the heat sink 114 while efficiently spreadinghorizontally, and the radiation efficiency can be raised. Thus, thereliability of the electronic device can be improved.

As described above, according to the present embodiment, between thesemiconductor element and the heat spreader and between the heatspreader and the heat sink, the carbon nanotube sheet according to thefirst or the second embodiment, which includes carbon nanotube bundlesoriented vertically to the film surface of the sheet, and the graphitelayer of graphite of the layer structure parallel to the film surface ofthe sheet, whereby the thermal conductivities between them can bedrastically improved. Thus, the radiation efficiency for the heatemitted from the semiconductor device can be raised, and the reliabilityof the electronic device can be improved.

A Sixth Embodiment

An electronic device according to a sixth embodiment will be describedwith reference to FIG. 19.

FIG. 19 is a perspective view illustrating the structure of theelectronic device according to the present embodiment.

In the present embodiment, the electronic device using the carbonnanotube sheet according to the first or the second embodiments as athermal conductive sheet which functions also as an electric conductivesheet will be described.

As illustrated in FIG. 19, an HPA (High Power Amplifier) 120 used inradio communication stations, etc. is incorporated in a package 122, anda heat sink 124 is jointed to the underside of the package 122. The heatgenerated from the HPA 120 is radiated to the heat sink 124 through theunderside of the package 122. The package 122 is also used as theelectric ground (ground surface) and is connected also electrically tothe heat sink 124. To this end, for the junction between the package 122and the heat sink 124, good conductor for electricity and heat is used.

As illustrated in FIG. 19, the carbon nanotube sheet 126 according tothe first or the second embodiment is used at the junction between thepackage 122 and the heat sink 124, whereby the package 122 and the heatsink 124 can be electrically connected to each other. Also, the heatgenerated from the HPA 120 can be efficiently conducted to the heat sink124, and the radiation efficiency can be improved. Thus, the reliabilityof the electronic device can be improved.

As described above, according to the present embodiment, between thepackage of the HPA and the heat sink, the carbon nanotube sheetaccording to the first or the second embodiment, including the carbonnanotube bundles oriented vertically to the film surface of the sheet,and the graphite layer of graphite of the layer structure parallel withthe film surface of the sheet formed between the carbon nanotube bundlesis arranged, whereby the thermal conductivity between them can bedrastically improved. Thus, the radiation efficiency for the heatemitted from the semiconductor element can be improved, and thereliability of the electronic device can be improved. Also, the highpower amplifier and the heat sink as the ground can be electricallyconnected to each other.

Modified Embodiments

Embodiments have been explained above, but the conditions andconstitutions of the respective embodiments are not essential. Theembodiments can cover other various modifications.

For example, in the above-described embodiments, examples of the sheetstructures and the semiconductor device using carbon nanotube weredescribed, but the embodiments are applicable widely to sheet structuresand semiconductor devices using linear structures of carbon atoms. Thelinear structures using carbon atoms can be, other than carbon nanotube,carbon nanowire, carbon rod, carbon fiber. These linear structures aredifferent from carbon nanotube in the size but are the same in otherrespects. The embodiments are applicable to sheet structures andsemiconductor devices using such linear structures.

The constituent materials and the manufacturing conditions described inthe above-described embodiments are not limited to those described aboveand can varied suitably to ends, etc.

The uses of the carbon nanotube sheet are not limited to those describedin the embodiments described above. The described carbon nanotube sheetis applicable, as the heat conductive sheet, to, e.g., the heatradiation sheet of CPUs, high power amplifiers of radio communicationstations, high power amplifiers for radio communication terminals, highpower switches for electric motors, servers, personal computers, etc. Byutilizing the high allowable current density of the carbon nanotubes,the carbon nanotube sheet can be applicable to vertical interconnectingsheets and various applications using the vertical interconnectionsheets.

In the above-described embodiments, as the catalytic metal film havingthe base film, the layer structures of Co film/TiN film and Co film/TiO₂film are described, but the catalytic metal film is not limited to them.For example, when a hydrocarbon-based raw material gas is used, with Co,Ni or Fe as the catalyst species, Ti, TiN, TiO_(x), TiSi, Ta, TaN, Zr,Hf, V, Nb, W or others can be used as the base film. When Fe is used asthe catalyst species, Al or Al₂O₃ can be also used as the base film.When an alcohol-based raw material gas is used, with Co used as thecatalyst species, Mo or others can be used as the base film.

The structures and the semiconductor device described in the third andthe fourth embodiments, and the electronic devices described in thefifth and the six embodiments, and their manufacturing methods aredescribed as the typical examples and can be suitably modified asrequired.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiments of the presentinventions have been described in detail, it should be understood thatthe various changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention.

1. A sheet structure comprising: a plurality of linear structure bundlesincluding a plurality of linear structures of carbon atoms arranged at afirst gap, and arranged at a second gap larger than the first gap; agraphite layer formed in a region between the plurality of linearstructure bundles and connected to the plurality of linear structurebundles; and a filling layer filled in the first gap and the second gapand retaining the plurality of linear structure bundles and the graphitelayer.
 2. The sheet structure according to claim 1, further comprising:a linear structure layer formed in the region between the plurality oflinear structure bundles, including a plurality of linear structures ofcarbon atoms, and having one ends of the plurality of linear structuresconnected to the graphite layer.
 3. The sheet structure according toclaim 2, further comprising: a plurality of the linear structure layersand a plurality of the graphite layers, wherein the linear structurelayers and the graphite layers are alternately stacked.
 4. The sheetstructure according to claim 1, wherein the plurality of linearstructures forming the plurality of linear structure bundles arerespectively oriented in a direction of a film thickness of the fillinglayer.
 5. The sheet structure according to claim 1, wherein the graphitelayer has a layer structure parallel to a surface of the filling layer.6. The sheet structure according to claim 1, wherein both ends of said aplurality of linear structure bundles are exposed on surfaces.
 7. Thesheet structure according to claim 1, wherein one surface of thegraphite layer is exposed on a surface.